Interference management is a key problem in multi-tier wireless communication systems. Due to limited spectrum available for cellular system, multi-tier cells may use the same frequency carrier which may cause co-channel interference. In addition, a multi-tier system may include heterogeneous cells. For example, some of the cells (e.g., femtocell base station) can be of a type of Closed Subscriber Group (CSG) which only allows subscribers to access the cell. When a femtocell base station (FBS), such as a CSG FBS, operates at the same frequency allocation (FA) or carrier frequency as the overlay macrocell base station, a subscriber station (SS) that is serviced by the BS (but is not a member of the overlaid CSG femtocell) may encounter interference caused by the CSG FBS as it gets close to the CSG FBS, such that its connection with the MBS may be weakened or disconnected.
Furthermore, if the CSG PBS is closed to non-members (i.e. it s a CSG-Closed FBS), the SS cannot handover to the CSG FBS. That is, the SS encounters interference from the CSG FBS such that it may be in a coverage hole. In this situation, interference mitigation (IM) is needed for both downlink (DL) and uplink (UL) control and data channels to provide the SS with a satisfied Quality of Service (QoS) while the CSG FBS can still have good coverage.
Therefore, there is a need in the art to better support IM in a wireless communication system. In particular, there is a need for a method and apparatus that use robust triggers to initiate and terminate IM that can be used by all types of base stations.